/Engine/Plugins/Online/OnlineSubsystem/Source/Public/Interfaces/OnlineGroupsInterface.h
Tells the server to remove the context user from the specified group. Should always result in the user's role for that group becoming Unaffiliated. Owners cannot leave their group, use TransferGroup (followed by LeaveGroup) or DeleteGroup instead.
void LeaveGroup ( const [FUniqueNetId](API\Runtime\CoreOnline\Online\FUniqueNetId) & ContextUserId, const [FUniqueNetId](API\Runtime\CoreOnline\Online\FUniqueNetId) & GroupId, const [FOnGroupsRequestCompleted](API\Plugins\OnlineSubsystem\Interfaces\FOnGroupsRequestCompleted) & OnCompleted )